NetStream Packet Sampling
Packet sampling takes samples of incoming and outgoing traffic in adjustable intervals so that only the statistics of sampled packets are collected. This reduces the impact of NetStream on device performance and the statistics show the flow status of the entire network.
The switch supports packet-based regular sampling. In this mode, one packet is sampled out of a fixed number of packets. For example, if the number of packets is set to 100 and packet sampling starts from the 5th packet, the 105th packet is sampled and so on. This mode is applicable to accounting based on traffic volume.
Calculation of the NetStream Sampling Ratio
The NetStream sampling ratio is related to the packet processing capability of NetStream, number of interfaces with NetStream sampling configured, sampling direction, interface rate, and average packet length on the network.
The minimum NetStream sampling ratio is calculated as follows:
When NetStream sampling is configured only in the outbound or inbound direction, the forwarding bandwidth (in Gbit/s) is calculated as follows:
Forwarding bandwidth = Number of interfaces with NetStream sampling configured x Interface rate
When NetStream sampling is configured in both the outbound and inbound directions, the forwarding bandwidth is calculated as follows:
Forwarding bandwidth = Number of interfaces with NetStream sampling configured x Interface rate x 2
For example, when NetStream sampling is configured on four XGE interfaces in the inbound direction and on another six XGE interfaces in the outbound and inbound directions, and these interfaces work at the maximum rate, the forwarding bandwidth is 160 (4 x 10 + 6 x 10 x 2) Gbit/s.
- The average packet length specifies the average length of packets on the network, in bytes.
- 20 indicates the length of the interframe gap (IFG) and preamble, in bytes.
- The packet processing capability of NetStream is described as follows.
- S5720-HI: 7.5 Mpps
- S6720-HI, S5732-H, S6730-H,?S6730S-H, S6730-S, and S6730S-S: 4.5 Mpps
- S5730-HI, S5731-H, S5731S-H, S5731-S, and S5731S-S: 2.25 Mpps